Chlorite-permanganate cellulosic bleaching process



FIPSSO? OR 398551883 SEARCH RQGM May 22, 1962 R. R. HEINZE ETAL 3,035,883

CHLORITE-PERMANGANATE CELLULOSIC BLEACHING PROCESS Filed Nov. 15, 1959 CLQTH WET 0.257o TO 3% WETTl N6 PERMANGANATE BATH SOLUTION V CLDTH WET WITH 5 TQ 20 /0 CHLORITE AND PERMANGANATE PERMANGANATE 0N CHLORITE m; a 20 TO 100 c STORAGE BLEACHED CLOTH RINSE REDUCING AGENT RINSE WATER INVENTORSI BLEACHED RSQ%*A E.%S'%%'B%Y NSN AND RINSED A CLOTH AGENT United States Patent 3,035,883 CHLORITE-PERMANGANATE CELLULOSIC BLEACHING PROCESS Richard R. Heinze, Ransomville, and Robert L. Ostrozynski, Lewiston, N.Y., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Nov. 13, 1959, Ser. No. 852,633 1 Claim. (Cl. 8-109) This invention relates to the bleaching of cellulosic textiles and textile fibers with aqueous solutions of chlorites.

Sodium chlorite is used for bleaching cellulosic materials because it is effective and economical; however it has one characteristic which requires improvement, i.e. the bleaching action is not satisfactory unless the solution is acidified to a pH of about 4 or less. Such acidification makes the solution unstable and bleaching is accompanied by the evolution of chlorine dioxide. The latter is a powerful irritant to the eyes and respiratory system of people. Furthermore, it represents a loss of bleaching power, since the chlorite is being uselessly decomposed.

We have discovered that aqueous solutions of watersoluble chlorites can be induced to give good bleaching, at a pH above 4 with very little chlorine dioxide evolution, by bringing a water soluble permanganate into contact with the chlorite solution after the latter has permeated the substance to be bleached. The permanganate, although used in a quantity insuflicient to effect any bleaching itself, causes the chlorite to bleach better and faster. This invention is useful in bleaching textiles woven from regenerated cellulose fibers (rayon), cotton fibers and linen fibers. Although sodium chlorite and potassium permanganate are the most common forms of these substances, this invention can be practiced with any water-soluble permanganate and any water-soluble chlorite. The alkali metal and alkaline earth metal chlorites and the permanganates are preferred. Although some chlorites give less bleaching than others the use of a permanganate according to this invention will improve the whiteness obtained with any chlorite over that obtained by the same chlorite when no permanganate is used. Broadly, the new method involves impregnating the cellulosic material with an aqueous solution of a water-soluble chlorite such as those of the alkali and alkaline earth metals, applying a small amount of a dilute aqueous solution of a water-soluble permanganate to the textile fibers after removing them from the location of chlorite impregnation, holding them for a period sufficient to allow the bleaching action to be completed, immersing the material in a dilute aqueous solution of a reducing agent and finally rinsing it in water and drying it.

In the first step, the cloth or fiber is wetted with an aqueous solution containing between 0.3% and 3% by weight of a water-soluble chlorine. Examples of some suitable chlorites are those of lithium, potassium, sodium, calcium, barium and strontium. The wetting can be done by spraying the solution on the cloth or by putting the cloth in a chlorite bath. This bath should not be alkaline and must be made slightly acidic with almost any acid, for example, formic, acetic, hydrochloric or sulfuric. The preferred pH range is about 4.5 to 7. There is no problem with chlorine dioxide evolution in this pH range. The substance being bleached should finally contain about 50% to 100% by weight, based on its own weight, of the chlorite solution. Certain exceptionally absorbent cloths such as huckaback toweling can hold up to twice their weight of liquid and can be impregnated with well over 100% by weight of the chlorite solution. If the cloth has been immersed in a chlorite bath, the excess liquid must be removed, for example by pressing or "ice wringing. If this is not done it will drip when the permanganate solution is applied, thus losing the active agents and resulting in poorer bleaching. The range of chlorite applied is about 0.25% to 3% by weight based on the weight of the material being bleached. Different types of cloth require different amounts of chlorite to attain a maximum whiteness, e.g. a heavy linen may require twice as much as a light cotton; however those skilled in the art of bleaching are familiar with the requirements of various cellulosic textiles and textile fibers.

The substance impregnated with the aqueous chlorite is next impregnated with a dilute solution of a water soluble permanganate to the extent of 0.5% to 20% by weight based on the weight of the chlorite thereon. Although more than 20% can be used, it is uneconomical and not any more effective. This small amount of permanganate can also be applied by spraying or dipping. Textiles and fibers can conveniently be passed between horizontal rolls wherein the bottom roller is partially immersed in the permanganate solution (dip-roll method), by rapidly passing the textile or fiber through an aqueous permanganate bath and wringing it to contain the desired amount of permanganate. The latter method may tend to leach some of the chlorite solution out of the cloth. The dip-roll method is preferred because of convenience.

Only the bottom roller need be wet because a slight pressure between the rollers causes the permanganate solution to permeate the cloth quickly. The permanganate solution is conveniently applied in the form of a 0.005% to 0.5% by weight aqueous solution. The amount applied is dependent upon the chlorite on the cloth; however about 10% to 50% by weight of the solution, based on the weight of the cloth is usually suflicient if the permanganate concentration of the solution is within the above limits. Since most cellulosic textiles and fibers cannot retain more than about 150% by weight of liquid without dripping, it is preferable not to use permanganate and chlorite solutions which are both in the lower end of the concentration ranges disclosed above. It is preferred not to exceed about 120% by weight of liquid on the cloth or fiber. Permanganates, in contrast to manganese salts, cannot be added to the chlorite solution because they are reactive with chlorites and quickly cause them to lose their bleaching power. Thus, manganous chloride or sulfate can be added to a chlorite bath to effect some improvements in bleaching; however a permanganate employed in this way causes the bath to become exhausted, by chlorine dioxide evolution, more quickly than it would have otherwise.

After the cloth is wet with the chlorite and permanganate solutions, it is stored until bleaching is complete. This process is greatly accelerated by heat; a humid atmosphere at about 50 to C. for A2 to 3 hours is excellent. The humidity can be supplied by applying the heat in the form of steam in a steam box or it can arise by evaporation of a minor amount of the water on the cloth if it is in a container of small volume which is is quickly saturated with water vapor. The solution on the cloth should not lose a material proportion of water, however, because the bleaching is preferably effected by dilute chlorite solutions.

When the holding period is over, the cloth is passed through a dilute solution of a reducing agent elfective to convert the manganese compounds on the cloth to soluble salts of manganese. The latter are white while the former are water-insoluble brown stains. A solution of 0.3% to 1% of such agents as hydrogen peroxide, oxalic acid, alkali metal sulfite or hydrosulfite is adequate. This being done, the cloth is rinsed in water and conventionally dried.

For any given textile or fiber, the process of this invention produces an exceptional whiteness more quickly and with less chlorite than prior processes. The following examples further illustrate this invention:

Examples 1-7 In the Examples 1 through shown in the table below,

5 in chlorite solutions.

Examples 1-7 Activator KMnO4 Mg(MnO4)2. NaMnO4.. KMnO4... KMnO4 MnClz. MnCLr. Percentby Wt. on cloth 0.2 0. 0.28 0.01 0.005 0.01 0.005 Percent NaClO: on clo h 0. Q5 1. a 2 1 1 1 1. EH of Ohlorite B 6 5. 5. 6 6 fl 6. eating time, Hrs 1 a 2 1 1 1 1 Heating temp C 96 60 R0 100 100 100. Final Bri htness 88 83. 6 8G. 4 81. 9 81. 1 72. 0 72. 9. Initial Brightness of clo 59 6% 61 57 57 67 57. Type of cloth Cotton Rayon Rayon-. Cotton- Cotton- Cotton- Cotton- Broad- Pophn Poplin Poplin. Poplin cloth.

the cloth lndlcated was treated according to this inven- We cla1m:

tion. It was impregnated with dilute solution of chlorite and activators of the type and to the extent shown. After the heating period of these cloths were passed through a 0.5% by weight oxalic acid solution, rinsed thoroughly in water and the reflectance was measured using a Photovolt Brightness Meter equipped with a tristimulus blue filter. With the brightness scale used, a difierence of 2 is noticeable to the unaided eye, while a dilference of 10 units represents a striking difference in whiteness. Examples 6 and 7 are included in the table below to show the inferior brightness obtained using a manganese salt under conditions comparable with using a permanganate of the present invention.

In order to compare the rates of decomposition of sodium chlorite in the presence of manganese salts and in the presence of permanganates, 4 aqueous solutions each containing 1.6% by weight of sodium chlorite were acidified with acetic acid to a pH of 5.5. Six hundredths of a gram of potassium permanganate, manganous sulfate or manganous chloride were placed in each of three of the solutions, the fourth serving as the blank. Periodic analysis .of the solutions for available chlorine was carried out. It was found that after 1.5 hours, the blank, the manganous sulfate and the manganous chloride samples had lost none of their available chlorine. During this time the sample containing the potassium permanganate lost over 9% of its originally available chlorine. Furthermore the addition of the permanganate to the chlorite A process for bleaching cellulosic textiles and textile fibers which comprises wetting them with an acidified, aqueous solution of a water-soluble chlorite having a pH between about 4.5 and 7, to apply 0.25% to 3% by weight of the chlorite to the cellulosic material, further wetting said material while containing chlorite thereon with an aqueous solution of a water-soluble permanganate to introduce 0.5% to 20% of the permanganate based on the weight of the chlorite, holding the thus wetted textile containing both chlorite and permanganate at a temperature of about 20 C. to 100 C. for about 0.5 to 3 hours and rinsing the material in a dilute aqueous solution of a reducing agent and then in water.

References Cited in the file of this patent OTHER REFERENCES White et :al.: Industrial and Engineering Chem., July 1942, 34:7, pp. 782-792.

Casciani: Paper Trade 1., :10, pp. 22, 24, 26, 28, 30 and 32.

Matthews: Bleaching and Related Processes, Chemical Catalog Co., New York, 1921, pp. -147, 367-370.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,035,883 May 22., 1962 Richard R. Heinze et 31.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 49, after "textile" insert or" line 56, for "chlorine" read chlorite column 2 line 58,, strike out "is' i column 3 line 23,, strike out 'offl,

Signed and sealed this 25th day of September 1962 (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

